Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B20/00—Processes specially adapted for the production of quartz or fused silica articles, not otherwise provided for
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/06—Glass compositions containing silica with more than 90% silica by weight, e.g. quartz
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/10—Forming beads
  • C03B19/1005—Forming solid beads
  • C03B19/106—Forming solid beads by chemical vapour deposition; by liquid phase reaction
  • C03B19/1065—Forming solid beads by chemical vapour deposition; by liquid phase reaction by liquid phase reactions, e.g. by means of a gel phase
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C12/00—Powdered glass; Bead compositions
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2201/00—Glass compositions
  • C03C2201/06—Doped silica-based glasses
  • C03C2201/08—Doped silica-based glasses containing boron or halide
  • C03C2201/10—Doped silica-based glasses containing boron or halide containing boron
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2201/00—Glass compositions
  • C03C2201/06—Doped silica-based glasses
  • C03C2201/20—Doped silica-based glasses containing non-metals other than boron or halide
  • C03C2201/23—Doped silica-based glasses containing non-metals other than boron or halide containing hydroxyl groups
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2203/00—Production processes
  • C03C2203/20—Wet processes, e.g. sol-gel process
  • C03C2203/26—Wet processes, e.g. sol-gel process using alkoxides

Definitions

• the present invention relates to a synthetic silica glass powder which is useful as a starting material for a very high purity silica glass product which is useful in the fields of producing semiconductors and optical fibers, particularly for use at a high temperature region of at least 1000° C. and which undergoes no substantial bubbling during the fusing operation.
• an alkoxysilane is used as a starting material, and such an alkoxysilane is hydrolyzed and subjected to a sol-gel method to obtain a silica powder, and then the silica powder is calcined to obtain a glass powder, which is then melted for vitrification to obtain the desired glass product.
• the alkoxysilane as the starting material can readily be purified by distillation, whereby a glass product of high purity can be obtained.
• silanol groups which the starting material has during the hydrolysis and gelation will remain as residual silanol groups in the particles after the calcination, whereby, as compared with natural quartz sand, the product has a higher silanol content.
• the silanol content is high, the viscosity at a high temperature tends to be low, and such a product is not useful for e.g. a diffusion furnace for semiconductors or for a crucible for drawing a silicon single crystal (Japanese Unexamined Patent Publication No. 320232/1989).
• the silanol content is at most 100 ppm, preferably at most 50 ppm.
• Japanese Unexamined Patent Publication No. 289416/1990 Japanese Unexamined Patent Publication No. 289416/1990 which comprises a first step of removing the majority of internal silanol groups (infrared absorption wavelength: about 3670 cm -1 ) at a temperature of from 600° to 1000° C. in an atmosphere with a low steam partial pressure, and a second step of removing isolated silanol (freely vibrating hydroxyl groups on the surface) groups (infrared absorption wavelength: about 3740 cm -1 ) at a temperature of at least 1200° C.
• bubbles With respect to silica glass parts to be used for optical fibers or semiconductors, presence of bubbles will be problematic in addition to the requirement for the strength at high temperature. Namely, if bubbles are present, in the case of e.g. a crucible for withdrawing a silicon single crystal, the bubbles are likely to break on the inner surface of the crucible during drawing of the single crystal, whereby defects will be caused by unstable surface of molten silicon, and the yield will be low. Further, when heated, the bubbles tend to expand, thus leading to a problem also in the dimensional stability. On the other hand, in the case of optical fibers, problems such as attenuation of the optical information or breakage of the optical fibers during the manufacturing are likely to result due to the presence of bubbles.
• the present inventors have conducted an extensive research to solve the above problem and as a result, have found that bubbling during the fusion will be little when the contents of morphologically different two silanols (internal silanol group and isolated silanol group) are within certain specified ranges in a silica glass powder containing a certain specific amount of boron.
• the present invention has been accomplished on the basis of this discovery.
• the present invention provides a synthetic silica glass powder obtained by calcining a silica gel powder obtained by hydrolysis of a tetraalkoxysilane, said synthetic silica glass powder containing from 1 ⁇ 10 -1 to 1 ⁇ 10 -4 ppm of boron and having an internal silanol group concentration of at most 150 ppm and an isolated silanol group concentration of at most 5 ppm.
• the synthetic silica glass powder as an object of the present invention is a silica glass powder obtained by drying and calcining a silica gel obtained by hydrolysis of an alkoxysilane.
• the hydrolysis of an alkoxysilane by a sol-gel method is carried out by reacting an alkoxysilane with water in accordance with a well-known method.
• the alkoxysilane to be used as the starting material is preferably a C 1-4 lower alkoxysilane such as tetramethoxysilane or tetraethoxysilane, or its oligomer.
• boron is incorporated in an amount of from 1 ⁇ 10 -1 to 1 ⁇ 10 -4 ppm, preferably from 5 ⁇ 10 -2 to 1 ⁇ 10 -4 ppm, based on the final synthetic silica glass powder.
• the boron concentration can be controlled to be within the above range by removing boron by controlling the distillation and purification conditions for the alkoxysilane.
• the boron concentration may be adjusted by adding e.g. an alkoxide of boron.
• the amount of boron contained in the synthetic silica glass powder can readily be measured, for example, by ICP-MS.
• the amount of water to be used is selected usually within a range of from 1 to 10 equivalent to the alkoxy group in the alkoxysilane.
• an organic solvent missible with water such as an alcohol or an ether
• a typical example of the alcohol to be used may be a lower aliphatic alcohol such as methanol or ethanol.
• an acid such as hydrochloric acid or acetic acid, or an alkali such as ammonia
• an acid such as hydrochloric acid or acetic acid, or an alkali such as ammonia
• a catalyst for the hydrolysis reaction, an acid such as hydrochloric acid or acetic acid, or an alkali such as ammonia, may be employed as a catalyst.
• materials to be introduced to this reaction system such as the starting material alkoxysilane, water, the catalyst, etc., are all of high purity.
• the obtained gel may be dried after pulverization, or may be pulverized after drying.
• the average particle size of the dried silica gel is usually from 50 to 1000 ⁇ m, preferably from 90 to 600 ⁇ m.
• the gel is dried to such an extent that the content of H 2 O is usually from 1 to 30 wt %. Drying is carried out usually by heating the gel at a temperature of from 100° to 200° C. under vacuum or in an inert gas atmosphere.
• the dried silica gel powder thus prepared is further calcined usually for from 10 to 30 hours by changing the temperature within a range of from 700° C. to 1200° C. to obtain a synthetic silica glass powder.
• the calcination conditions (the calcination temperature, the calcination atmosphere, etc.), it is possible to adjust the internal silanol and the isolated silanol contained in the synthetic silica glass powder.
• the synthetic silica glass powder of the present invention is adjusted so that the internal silanol would be at most 150 ppm, and the isolated silanol would be at most 5 ppm. Even if the internal silanol is higher than the conventional value (higher than 100 ppm), so long as the isolated silanol is at most 5 ppm, formation of bubbles can remarkably be reduced. To further reduce formation of bubbles, it is preferred to control the above-mentioned isolated silanol to a level within a range of from about 0.05 to 2 ppm. Further, the internal silanol is preferably at most 140 ppm, more preferably within a range of from 5 to 80 ppm.
• the synthetic silica glass powder thus obtained has a merit that formation of bubbles during the fusion is little, and it can be suitably used as a starting material for a very high purity silica glass product, which is free from formation of bubbles, such as a crucible for withdrawing a silicon single crystal, or a tube or jig for a diffusion furnace for manufacturing semiconductors.
• tetramethoxysilane selected so that the boron content of the resulting synthetic silica glass powder would be 2 ⁇ 10 -2 ppm, and water in an amount corresponding to five times in equivalent to the tetramethoxysilane, were charged and stirred for one hour at a temperature of 30° C. for hydrolysis to obtain a uniform sol.
• This sol was transferred to a butt made of polyvinyl chloride and left to stand for 5 hours for gelation.
• the gel thereby obtained was dried for 12 hours at 140° C. by means of a vacuum drier, and then the particle size adjustment was carried out to a particle size of from 100 to 500 ⁇ m.
• this synthetic silica glass powder was dissolved in hydrofluoric acid, and the solution was adjusted, whereupon the boron concentration was measured by ICP-MS and found to be 2 ⁇ 10 -2 ppm. Further, this synthetic silica glass powder was formed into an ingot of 12 mm ⁇ 60 mmH, by means of a Verneuil's method fusing apparatus by oxygen-hydrogen flame, whereby only three very tiny bubbles were visually observed.
• a dried silica gel powder was prepared in the same manner as in Example 1, and 100 g of the powder was charged into a cylindrical quartz container of 80 mm ⁇ 60 mmH, which was then set into an electric furnace. Then, the temperature was raised to 1200° C. at a rate of 200° C./hr, and calcination was carried out at 1200° C. for 15 hours. After cooling naturally, the concentrations of the internal silanol, the isolated silanol and boron were measured in the same manner as in Example 1. The results are shown in Table 1. Further, an ingot of 12 mm ⁇ 60 mmH was prepared by the Verneuil's method, whereby no bubble was visually observed.
• a dried silica gel powder was prepared in the same manner as in Example 1 except that as the starting material, tetramethoxysilane prepared under a distillation and purification condition different from Example 1 was used, and 100 g of the powder was charged into a cylindrical quartz container of 80 mm ⁇ 60 mmH, which was set in an electric furnace. Then, the temperature was raised to 1100° C. at a rate of 200° C./hr, and calcination was carried out at 1100° C. for 55 hours. After cooling naturally, the concentrations of the internal silanol, the isolated silanol and boron were measured in the same manner as in Example 1. The results are shown in Table 1. Further, an ingot of 12 mm ⁇ 60 mmH was prepared by the Verneuil's method, whereby many bubbles formed.
• a dried silica gel powder was prepared in the same manner as in Example 1 except that as the starting material, tetramethoxysilane prepared under a distillation and purification condition different from Example 1, was used, and 100 g of the powder was charged into a cylindrical quartz container of 80 mm ⁇ 60 mmH, which was set in an electric furnace. Then, the temperature was raised to 1200° C. at a rate of 200° C./hr, and calcination was carried out at 1200° C. for 2 hours. After cooling naturally, the concentrations of the internal silanol, the isolated silanol and boron were measured in the same manner as in Example 1. The results are shown in Table 1. Further, an ingot of 12 mm ⁇ 60 mmH was prepared by the Verneuil's method, whereby many bubbles formed.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Geochemistry & Mineralogy (AREA)
• General Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Dispersion Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Glass Compositions (AREA)
• Glass Melting And Manufacturing (AREA)
• Silicon Compounds (AREA)

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Cited By (14)

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• 1994
  • 1994-07-11 JP JP6158755A patent/JPH0826742A/ja active Pending
• 1995
  • 1995-07-07 DE DE69500793T patent/DE69500793T2/de not_active Expired - Lifetime
  • 1995-07-07 EP EP95110680A patent/EP0692461B1/fr not_active Expired - Lifetime
  • 1995-07-07 AU AU24866/95A patent/AU684167B2/en not_active Ceased
  • 1995-07-10 KR KR1019950020206A patent/KR100219250B1/ko not_active IP Right Cessation
  • 1995-07-10 US US08/500,202 patent/US5604163A/en not_active Expired - Lifetime
  • 1995-07-11 TW TW084107171A patent/TW312686B/zh active

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